Failure of an anastomosis is one of the most significant problems in microsurgery. All existing techniques used to monitor transplanted tissue suffer from one or more problems. No technique is suitable for continuously monitoring tissue that is buried below the surface. The ultimate goal of this project is a monitoring device which overcomes the problems of existing techniques. Our goal in Phase I is to prove feasibility of a monitor using a miniaturized ultrasonic transducer mounted at the tip of a catheter, and placed next to an anastomized vessel with a suture attachment. Blood flow will be monitored for several days post-operatively and then the catheter will be withdrawn. Blood flow in the vessel will be detected by use of Doppler techniques. The ouptput of the instrument will be continuous measures of blood flow and stenosis, in one or more vessels. We will adapt blood flow quantification methods developed for transcutaneous measurement and ultrasonic catheter designs developed for endoscopic applications (1.8 mm OD) for this purpose. Blood flow measurements using Doppler ultrasound classically suffer from dependencies on angle, vessel size, velocity profile across the vessel, and signal attenuation. We will attempt to minimize these dependencies by taking advantage of the close and controllable proximity of the probe to the vessel being studied. Accuracy of measurement will be assessed by animal bleeding studies. Data will be gathered in the clinic using experimental catheters during micro-surgical procedures and postoperative recovery. The ultimate benefit of this monitor will be the prognostic value in indicating need to intervene in a failing anastomsis. Clinical value will be evaluated by comparing results with other monitoring methods (clinical appearance, laser Doppler, and PO2), and with the clinical case histories. The commercial potential of this device can be sizable when combined with other applications for quantifying Doppler, so that a cost effective and commercially viable product can be made available to those who need it.